Cells and batteries are energy storage devices well known in the art. Cells typically comprise electrodes and an ion conducting electrolyte therebetween. For example, the rechargeable lithium ion cell, known as a rocking chair type lithium ion battery, typically comprises essentially two electrodes, an anode and a cathode, and a non-aqueous lithium ion conducting electrolyte therebetween. The anode (negative electrode) is a carbonaceous electrode that is capable of intercalating lithium ions. The cathode (positive electrode), a lithium retentive electrode, is also capable of intercalating lithium ions. The carbon anode comprises any of the various types of carbon (e.g., graphite, coke, carbon fiber, etc.) which are capable of reversibly storing lithium species, and which are bonded to an electrochemically conductive current collector (e.g., copper foil) by means of a suitable organic binder (e.g., polyvinylidine fluoride, PVdF).
The cathode comprises such materials as transition metals and chalcogenides that are bonded to an electrochemically conducted current collector (e.g., aluminum foil) by a suitable organic binder. Chalcogenide compounds include oxides, sulfides, selenides, and tellurides of such metals as vanadium, titanium, chromium, copper, molybdenum, niobium, iron, nickel, cobalt, and manganese. Lithiated transition metal oxides are, at present, the preferred positive electrode intercalation compounds. Examples of suitable cathode materials include LiMnO2, LiCoO2, LiNiO2, and LiFePO4, their solid solutions and/or their combination with other metal oxides and dopant elements, e.g., titanium, magnesium, aluminum, boron, etc.
The electrolyte in such lithium ion cells comprises a lithium salt dissolved in a non-aqueous solvent which may be (1) completely liquid, (2) an immobilized liquid (e.g., gelled or entrapped in a polymer matrix), or (3) a pure polymer. Known polymer matrices for entrapping the electrolyte include polyacrylates, polyurethanes, polydialkylsiloxanes, polymethacrylates, polyphosphazenes, polyethers, polyvinylidine fluorides, polyolefins such as polypropylene and polyethylene, and polycarbonates, and may be polymerized in situ in the presence of the electrolyte to trap the electrolyte therein as the polymerization occurs. Known polymers for pure polymer electrolyte systems include polyethylene oxide (PEO), polymethylene-polyethylene oxide (MPEO), or polyphosphazenes (PPE). Known lithium salts for this purpose include, for example, LiPF6, LiClO4, LiSCN, LiAlCl4, LiBF4, LiN(CF3SO2)2, LiCF3SO3, LiC(SO2CF3)3, LiO3SCF2CF3, LiC6F5SO3, LiCF3CO2, LiAsF6, and LiSbF6. Known organic solvents for the lithium salts include, for example, alkyl carbonates (e.g., propylene carbonate and ethylene carbonate), dialkyl carbonates, cyclic ethers, cyclic esters, glymes, lactones, formates, esters, sulfones, nitrates, and oxazoladinones. The electrolyte is incorporated into pores in a separator layer between the anode and the cathode. The separator layer may be either a microporous polyolefin membrane or a polymeric material containing a suitable ceramic or ceramic/polymer material. Silica is a typical main component of this latter type of separator layer.
Lithium ion battery cells, as are most cells, are often made by adhering, e.g., by laminating, thin films of the anode, cathode, and the electrolyte/separator layers together wherein the electrolyte/separator layer is sandwiched between the anode and cathode layers to form an individual cell. A plurality of such cells are generally bundled together, in what is typically known as a cell stack or winding, and packaged to form a higher energy/voltage battery. Packaging of the cell or cell stack generally involves a vacuum seal lamination process requiring complex packaging equipment. During packaging, the pressures and forces are exerted upon the individual cell layers, which may cause vulnerable edges and corners of the electrode layers in each cell to be bent, crushed or otherwise damaged. This damage often decreases the overall life and power of the cell. Specifically, damage to the electrode films results in non-uniform utilization of the active materials, which in turn, can lead to lithium plating and loss of life. In addition, the pressure exerted on the electrode layers may cause the separator to split thereby posing possible risks of shorting within the battery.
Thus, there is a need to develop a cell construct and method of assembly to produce a more robust battery cell having longer life and increased activity, and which is less prone to developing shorts.